Rangers are the main kiting class. Because they were originally scouts they actually maintain their ability to use stealth. Rangers are a tricky class as they maintain their melee abilities, a couple which are great to use defensively, but then they also gain all these new ranged abilities. Due to Aions weapon concept, a Ranger cannot have access to both their melee abilities at the same time as their ranged abilities; they must take the half second or so to swap their weapons. Rangers focus on kiting, traps, and not much else. Even killing a mob in PvE on their own can require kiting since they do not have a pet. There is nothing stopping a Ranger from using their bow in melee range, but without any real tanking defenses and a very limited health pool, it is not a good idea. One of the more interesting things to do with rangers is jump shooting. It is possible to run at full speed away from a target using jump turning to continually pour arrows into them. There are also a few issues with animation canceling on some of the casted shots, essentially removing the cast time and therefore allowing you to maintain your mobility.
Rangers focus on single target ranged damage, and it takes them quite awhile before even gaining access to an AoE attack. Traps are single target and can either root targets in place or deal extra damage, there is even a special one which increases the cast time of anyone stuck in it, so an anti-caster trap. They have access to a ranged stun, a ranged silence, as well as a ranged snare. Rangers also gain one of the same defensive abilities that Sorcerers have in the form of a backwards teleport. Offensively on the other hand, they are a little like Gladiators in that their critical damage hits from their bows can knock back a target, temporarily stunning them.
They are actually rather sore when it comes to crowd control, since they are never meant to be that close to the action in the first place. All of their crowd control is single target, so attempting to fight multiple players, or even just multiple mobs, is difficult. They lack health and their only real defense is range. One thing that is really fun about them though is their ability to transform into a Mau. A furry creature that can run faster and deal increased damage, a Ranger in Mau form is basically the ultimate kiter.
Sorcerers are direct damage magic users. They employ a large amount of magical snares, immobilizers, and knockbacks to keep their targets at range. All of their abilities focus around the four elements in the game, Earth, Air, Water, and Fire. Fire is typically used for direct damage, Water for damage and crowd control, Earth as damage over time abilities and self buffs, and then Air for debuffs. Like most magic casters in MMO games, Sorcerers suffer from an acute lack of health. They can teleport backwards to escape from danger, surround themselves with an earthen shield to absorb damage, or freeze in a block of ice to make them immune to everything. They are one of the better anti-melee classes in the game, having the hardest time with Assassins but they can deal fine with Gladiators or Templars.
While they deal direct damage they do have a couple AoE spells. They also have a large amount of offensive crowd control. They can put targets to sleep with a casted spell, and then use AoE root spells to hold their targets in place, as well as their ranged knockbacks and stuns that can be chained off of some of their water spells. They even have an instant cast ranged snare and can choose to eventually learn an AoE sleep spell if they want. Even with all this, the Sorcerer truly shines when it comes to damage dealing. Assassins and Rangers may deal higher burst damage over a couple seconds, but given a little more time to cast and the Sorcerer will easily out do them. They are the highest single target damage dealing class in the game.
Spirit masters are the only pet class in Aion. Pets level up with the player and actually transform from rather ugly looking blobs into majestic creatures at the maximum level. I have not seen any max levels in game, for obvious reasons, but if you have not seen them yet look them up, I will probably end up leveling a Spirit master just to watch the pets grow. Spirit masters rely on their pets to a large degree, each pet helping out the player in different situations. Unlike the Sorcerer who focuses on direct damage spells, the Spirit master works with damage overtime spells.
Spirit masters do not have a large amount of roots or immobilize abilities, but they have a few, and they can also cause targets to run away in fear. Spirit masters are also best at debuffing their targets to magical damage, removing targets resistances to different elements, allowing themselves, their pets, and Sorcerers to deal more. Their largest weakness is the lack of kiting tools they have, where the Sorcerer can usually run forever, the Spirit master will probably end up snared and stuck trying not to die. They are the only class that can offensively remove buffs from a target though, as well as really put up a lot of debuffs. They can self heal by dealing damage to a target and absorbing a portion of the enemies health. The pets are not there just for show and minor damage, a good number of the Spirit masters spells, some of the most powerful, can only be cast through these pets, so if you are into that kind of added micro management then this is a good class for you. How they eventually compare in damage to the other DPS classes I am really not sure, but I cannot imagine it being a problem.
Clerics are the healing class in Aion. Like the Templar is the tank, the Cleric is the healer. As a class they give up many offensive abilities so that they can heal. AoE heals, single target large heals, instant heals, heal over times, the Cleric has access to all of it. They are also the only class that can purge harmful magic from friendly players. Their offense is relegated to a few holy spells and the ability to summon stationary damage pets, so Clerics are best played in groups where they can offer support instead of try to take on everything themselves.
They have a couple root spells to help them kite targets, but probably will not kill anything in PvP in a 1v1 situation. Of course they will not die either. They can sacrifice their own health to create defensive barriers that deal damage to attackers, and can even resurrect themselves if they die, as well as resurrect everyone else, eventually gaining access to a mass resurrection ability. Like the other classes, they continue to have access to the core abilities they learned as a Priest. While they do still have these melee abilities, they are best served using their ranged spells to deal damage. Both Clerics and Chanters gain a decent amount of protection from physical classes in the form of chain armor and the ability to equip shields. If you are looking to play a purely support class then a Cleric would be a good option.
Chanters are an offshoot of the Cleric that, rather than going after healing spells exclusively, also learns more about melee combat. Chanters are the best buff class in the game, from increased health to faster group speed movement and attack rate buffs as well. A few people have compared the Chanter to the traditional RPG class of the Bard. They can imbue their personal weapons with spells, increasing their damage output, as well as use aura type buffs to help out their allies. They have access to most of the healing spells a Cleric does, but cannot resurrect friends or cleanse debuffs from them.
Much like the Gladiator, Chanters tend to knock people down a lot with their giant staves, so just having one hitting you can be a danger in a group PvP situation. Chanters enjoy a stun and a few debuffs, but besides that they do not have access to any on demand crowd control. Instead they make themselves look like one of the worst targets to attack with their healing and high defensive rates, all while dishing out moderate damage in the form of spells or melee attacks. They offer mana back abilities that can be used mid combat for group members in case anyone is running low, and are a great utility class, but are not really one that can steal the show. Like the Cleric, a Chanter can be the backbone to a group, providing everything needed by a healer and more. Both the Cleric and the Chanter are healers, the main difference is if a player wants to be purely defensive or wants to provide some added offense at the price of healing ability.